Segmental grinding wheel



SEGMENTAL GRINDING WHEEL Filed April 18, 1935 a/ 3/ I2 42 I 43 I0 16 f? au- 34 \v THuRE LA R66 0 WITNESSES 32 3/ 66 ll) surface.

Patented Mar. 16, 1937 oNirE srr SEGMENTAL GRINDING WHEEL tionof Massachusetts ApplicationApril 18, 1935, Serial No..17,039

9 Claims. (01. 51-206) This invention relates to a grinding wheel, and

more particularly to a grinding wheel composed of bonded abrasive segments.

Heretofore, it has been proposed to construct large sized grinding wheels, such as pulpstones employed for producing wood. pulp, of a plurality of bonded abrasive segments or sectors, which cooperate to provide an abrasive annulus having a substantially continuous cylindrical grinding These segments are usually composed of granular abrasive material, such as silicon carbide or crystalline alumina, of suitable size and shape bonded together by means of various vitrified ceramic materials, such as porcelain or glass.

In view of the inherent fragile nature of such a bond, the segments are relatively weak, and consequently it is essential that they be rigidly and evenly supported in grinding position.

A grinding wheel employed for a pulp grinding operation is usually subjected to enormous grinding pressures, as well as severe internal stresses, due to the fact that its large diameter and heavy mass are rotated at a high speed to produce the desired grinding action. Furthermore, grinding wheels of this type may be frequently subjected to temperature variations from as low as zero degrees Fahrenheit to as high as that of the boiling point of water; In view of the fact that in many pulp grinding operations only a small amount of water is maintained within the grinding pit, these temperature changes are frequently quite rapid in large pulpstones and cause uneven expansions therein which result in wheel breakage. x

It is the primary object of this invention to provide a segmental type of grinding wheel which may be easily and inexpensively manufactured and wherein each of the abrasive segments may be free to individually and uniformly expand and contract to relieve any internal wheel stresses occasioned during grinding and thereby minimize wheel breakage.

It is a further object of this invention to provide a unitary type of segmental grinding wheel wherein the segments are individually and removably secured to a central rotatable support in such a manner that a single broken segment may be easily and quickly'replaced in the field without necessitating returning of the grinding wheel to the manufacturer for rebuilding.

It is a further object of this invention to provide a segmental grinding wheel construction wherein the segments cooperate in laterally supporting each other against the rotational thrusts of grinding and yet are free to individually expand and contract and be relieved of internal stresses occasioned by the heat of grinding.

To the accomplishment of these objects and such others as will be apparent to one skilled in the art, I have provided a segmental type of grinding wheel composed of a plurality of separately manufactured bonded abrasive sectors which may be rigidly fastened to a central support or hub in such a manner that each sector is free to individually expand under the influence of the heat of grinding and thereby prevent the accumulation of any stresses or strains within. the wheel. In order that the segments may be properly positioned and rigidly supported, each segment is provided with one or more anchoring devices imbedded within its base whereby it may be rigidly fastened to a central rotatable support independently of the other segments within the wheel. The anchoring devices may also include suitable clamping members which removably secure the segments to their central support under adjustable tension or, if desired, suitable elongated anchoring devices may be permanently imbedded within each of the segments and also within the central support integrally and fixedly securing the segments thereto. Each of the anchoring devices preferably embodies an elongated elastic tensioning member which serves to compensate for expansion and contraction within the wheel; but for some types of wheels this feature may be omitted. The segments are preferably mounted in spaced relation to each other and the interstices therebetween may be filled with a suitable material, which may be the same as that disclosed in my prior patents, or a deformable or compressible material which adheres to the opposed faces of the adjacent segments and compensates for lateral expansions of the individual segments towards each other as oocasioned by the heat of a grinding operation and also aids in laterally supporting the segments during the grinding operation.

The present invention is illustrated by the attached drawing wherein:

Fig. 1 is a fragmentary cross sectional view which is partly broken away to illustrate my preferred type of segmental wheel construction;

Fig. 2 is a fragmentary sectional view taken approximately along the line 2-2 of Fig. l; and

Fig. 3 is a sectional View showing a modified type of my grinding wheel.

In accordance with the preferred type of my invention, as illustrated in Figs. 1 and 2, I have provided a plurality of wheel sectors or segments H] which are assembled as an annulus on a central rotatable support to form a cylindrical grinding member, such as a pulpstone employed for producing wood pulp. These segments may be composed of abrasive grains, such as crystalline alumina, silicon carbide or other suitable abrasive grains bonded together into a desired wedge shaped or sector form by a suitable bond, such as a vitrified ceramic material. The segments are provided with outer arcuate abrading surfaces l2 which cooperate to form an operative peripheral wheel face i3, opposed side faces 55, end faces I6 and inner supporting faces 18 adapted to be seated on a rotatable central supporting member or hub 22, such as an iron drum or monolithic center composed of concrete or other suitable cementitious material cast in position. Each segment may be constructed as a separate article of manufacture independent of its support, and it is so made that it may be individually and removably fastened to the central support by suitable anchoring devices without weakening the segments or producing uneven internal stresses therein.

My preferred type of anchoring device, as illustrated in Figs, 1 and 2, comprises an anchoring member integrally fastened to and imbedded within the lower portion of each segment and adjustably secured to the central wheel support 20 by a clamping member. The anchoring members may comprise nuts 2!, each of which is imbedded within a recess 22 cast or otherwise suitably formed in the inner supporting face it of the bottom of each sector and permanently and rigidly secured thereto by a suitable material 24 cast in position, such as Babbitt metal, Portland cement, sulphur or other suitable cementitious medium which serves to fasten the nut integrally within the abrasive segment Ill. The nuts are preferably provided with knurled or suitably roughened outer faces 25 and the recesses 22 are provided with grooves, ridges or reentrant portions in their side faces to aid in integrally and permanently locking the anchoring members in position. One or preferably a plurality of clamping devices may be employed to secure each segment to the central support 20. These clamping devices are so located within the base of the segment that it will be uniformly secured in position.

As illustrated, each segment is seated in a predetermined position on a mating face 28 of the central supporting member 20 and in my preferred construction, the engaging faces l8 and 28 are flat to aid in evenly supporting and rotating the segments. To removably and rigidly fasten these segments in desired position, the imbedded nuts 2| within the lower portion of each segment are connected under a predetermined tension to an iron mandrel 30 within the central supporting member 29 by means of bolts 3| passing through the support 20 and through holes 32 within mandrel 36. The upper ends of bolts 31 are screw threaded into the imbedded nuts 2| and the lower ends extending through the holes 32 in mandrel 3!] have suitable clamping nuts 34 threaded thereon which engage the mandrel 3D and secure the required tension on bolts 3| to hold the segments in position under desired tension. Each bolt 3| is protected from the support 20 by means of a coating member 33 which may comprise a sheet of thin wax paper wrapped about the bolt or even a coating of wax or a film of oil thereon which prevents the shank of the bolt from adhering to the cementitious material of support 20 and permits the bolts to slide therein and provide suitable adjustable clamping pressures to hold the segments under desired tension. If desired, the bolts 3! may have certain elastic properties which compensate for radial expansions of the segments during grinding, as described in my prior Patent No. 1,736,161.

The clamping bolts 31 are so located that the segments H] are individually and securely mounted upon the central support 20 with their adjacent opposed side faces I5 and end faces I6 in predetermined spaced relation to each other. The interstices between the adjacent opposed faces are filled with a suitable compressible or deformable material 35 of the types shown in my prior Patents No. 1,736,161 and No. 1,815,108 or preferably a rubber compound which may be vulcanized in position and will adhere to the opposed segment faces. Such a rubber compound ,is preferably of the type commonly referred to by the term hard rubber having a sulphur content of at least 20% by weight, which provides a tough supporting body. This rubber is so compounded that it will soften and be subjected to a plastic fiow under the influence of heat. Hence, when the frictional heat of grinding causes lateral expansions of the wheel segments towards each other, this same heat of grinding serves to simultaneously soften the rubber filler to a deformable condition which will become easily compressed and so compensate for any lateral segment expansion and thus relieve excessive internal wheel stresses. Upon cooling, the rubber filler will again harden to a tough body which aids in lateral segment support. In my preferred construction, the rubber compound comprising the filling material 35 is suitably mixed with granular abrasive, such as crystalline alumina or silicon carbide, of desired size and shape disposed throughout its entire body so that after vulcanization, the entire wheel periphery will be provided with substantially the same abrading properties. One example of a suitable filling material 35 may comprise a rubber compound of the following consistency:

Per cent by weight Smoked sheet rubber 5O Sulphur 2'7 Granular silicon carbide 23 In the assembly of my preferred type of segmental grinding wheel shown in Figs. 1 and 2, I thread a clamping bolt 31 into each of the imbedded nuts 2| thereby integrally securing each bolt to a wheel segment. The protruding portion of each bolt which is to be encased within the central wheel support 20 is then encased in a coating member 33, such as a layer of waxed paper, after which the bolts are inserted through the corresponding holes 32 in the mandrel 30 and the segments are radially so located relative to the mandrel and to each other that they form an annulus surrounding the mandrel which is coaxial therewith but spaced therefrom. The holes within the mandrel receiving the bolts 3! have been so located and the segments constructed of such shape and size that the adjacent opposed plane faces of the adjacent segments provide substantially parallel spaced surfaces. During this assembly of the abrasive annulus, each of the crevices between the opposed faces of adjacent segments is filled with a sheet of suitable material 35, such as an unvulcanized sheet of hard rubber compound having granular abrasive material disposed throughout its body.

Nuts are threaded onto the inner end of bolts 3| and tightened against the inside peripheral face of the mandrel 30 to force thegrubber sheets into positive engagement with :the opposed segment faces and slightly compress said sheets therebetweenl The assembly of the imandrel and segments is then placed within an oven and subjected to a suitable heat such as 250 C. for several hours to vulcanize the rubber sheets in position betweenthesegments and cause them toadhere thereto and aid in supporting them as an integral grinding member wherein the individual segments may be free to laterally expand and contract slightly due to the deformable properties of the rubber under heat of grinding.

.Upon completion of the vulcanizing operation, the assembly is removed from the oven and cooled after which the space between the mandrel and the bottom segment faces I8 is completely filled with a suitable cementitious material, such as concrete or other suitable material, which may be cast in position to form the central wheel support 20. If desired, suitable reinforcing members may also be incorporated in the cement to strengthen the supporting body. After the cement has set, the nuts 2| may be tightened to clamp the segments in position under the desired pressure. The bolts 3| are free to slide within the support 20 and provide adjustment since the coatings 33 thereon prevent the cement from adhering thereto.

It will be appreciated that by providing a construction of this type, wheel breakage is minimized since any internal stresses within the segments will not be transmitted therebetween and accumulate throughout the wheel in view of the fact that the deformable material 35 and the elastic properties of bolts 3| will permit each segment to be individually relieved of its stresses and strains during grinding. Furthermore, in the event that wheel breakage should occur, one or more segments may be individually replaced in the field without necessitating shipping of the entire massive wheel back tothe factory to be completely rebuilt, as has been the prior practice. In a repair of this type, the broken segment is removed and the adjacent sheets 35 are stripped from position. During the insertion of a new segment, similar but partially vulcanized rubber sheets 35 may be placed between the adjacent segment faces and the heat of grinding will serve to further vulcanize said sheets inposition, or if desired the crevices between segments may be filled with other deformable material, such as a Babbitt metal which may be cast in position.

A modified form of my invention; asillustrated in Fig. 3 of the drawing, comprises a plurality of bonded abrasive wheel segments 40 of the same general size, material and shape as those disclosed in my preferred type of invention and provided with outer arcuate abrading surfaces 42, which cooperate to form an operative peripheral wheel face 43. The segments are also provided with opposed side faces which are preferably radial of the wheel, and the inner supporting faces 48 are adapted to be seated on a central support or hub 5|] composed of a suitable cementitious material, such as concrete, cast in position, in the same manner as shown in my preferred type of invention. Each segment is further provided with recessed or reentrant cavities 52 within which anchoring devices 54 are partially embedded and integrally secured by a suitable material 55 cast in position, such as. Babbitt metal, Portland cement, sulphur or other suitable cementitious for wheel expansions during grinding, as de scribed in my prior Patent No. 1,736,161. As illustrated, the upper end of each anchoring device including head 51 is embedded within the lower portion of a segment and integrally secured thereto by the material 55 cast thereabout, and the lower portion of the anchoring device including head 58 is embedded within the central cementitious support 50.

If desired, the cavities .52 may be provided, as illustrated, with grooves, ridges, or depressions 60, and the anchoring devices may be provided with rough or knurled outer surfaces which aid in interlocking the cast material 55 in position and maintaining the anchoring devices integrally fastened within the segments. As in my preferred type of invention, each segment is seated in. a predetermined position on a mating face 64 of the central supporting member 53 and the engaging faces 48 and 64 are preferably fiat to aid in evenly supporting and rotating the segments. The supporting member 50 is cast in position between a central mandrel 66 and the inner segment .faces 48 embedding the exposed ends of the anchoring devices therein and thus integrally securing the segments in desired annular position as an integral grinding member. Radial wheel expansion as caused by the centrifugal forces of wheel rotation coupled with the frictional heat of grinding is compensated for by the elastic properties of the elongated tension members 56. Lateral expansions of the individual segments towards each other is compensated for by suitable sheets of deformable or compressible material, as disclosed in my prior patents, and preferably sheets of rubber material 68 containing abrasive grains of silicon carbide or crystalline alumina and of the same type as the rubber sheets 35 which may be vulcanized in position between the segments in the same manner as in my preferred type of invention.

' In the manufacture of this modified form of my invention, the abrasive segments having the anchoring devices embedded therein and extending therefrom are assembled in the form of an annulus with the intervening sheets of rubber compound 68 located between adjacent segment side faces and secured in position by means of any suitable type of annular clamping members arranged to peripherally engage the segments. The assembled annulus of segments is then subjected to a suitable vulcanizing operation, as in my preferred type of invention, after which it is removed from the oven and permitted to cool. The central mandrel E6 is then located coaxial within the abrasive annulus and the space between the mandrel and the bottom segment faces 48 is completely filled with a suitable cementitious material, suchv as concrete, cast in position to form the central wheel support 50 which provides the segment supporting faces 64 and embraces the anchoring devices with sufficient tenacity to provide an integral unitary grinding wheel structure.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A grinding wheel comprising a plurality of bonded abrasive segments secured together in the form of an abrasive annulus, a rotatable central support therefor and an anchoring'device for each sector including an elongated elastic tension member which compensates for expansion and contraction within the wheel due to temperature changes, means at one end of the tension member which is embedded within a segment and integrally secured thereto and means to individually and removably secure the other end to the central support whereby each segment may be removably fastened in grinding position.

2. A grinding wheel comprising a plurality of bonded abrasive segments arranged in the form of an abrasive annulus, a rotatable central support therefor composed of a material which is cast in position within the annulus, and an anchoring device imbedded within the lower portion of each segment and secured to the central support which serves as the sole means to integrally fasten each segment to the central support.

3. A segmental grinding wheel comprising a plurality of bonded abrasive segments arranged in the form of an abrasive annulus, a rotatable central support therefor composed of a material which is cast in position and engages the bottom of each segment, an anchoring device for each segment having an elongated tension member which compensates for expansion and contraction within the wheel due to a temperature change, means at one end thereof which is secured to the support and means at the other end of the tension member imbedded within a segment and integrally secured thereto.

4. A grinding wheel comprising a plurality of separately manufactured bonded abrasive segments secured together in the form of an abrasive annulus, a rotatable central support therefor which is molded in situ and an elongated anchoring device for each segment, including an enlarged portion at one end thereof embedded Within the lower portion of a segment and an enlarged portion at its other end embedded within the central support, which serves to individually secure each segment in position on the rotatable support,

5. A grinding wheel comprising a plurality of bonded abrasive segments arranged in the form of an abrasive annulus having a cylindrical grinding face, a central supporting body of cementitious material cast in situ within the annulus and contacting with the inner segment faces, and a plurality of anchoring devices embedded within each segment and also within the cementitious body which rigidly secure the segments in position and form an integral grinding unit.

6. An abrasive wheel comprising a rotatable support, a plurality of bonded abrasive sectors individually secured thereto in spaced relation to each other and in the form of an annulus, a deformable material located within and substantially filling the crevices between the adjacent segments which compensates for lateral expansion of the individual segments, and an anchoring device securing each sector to the rotatable support having an elongated elastic tension member, means at one end of the tension member secured to the support and means at the other end thereof embedded within the lower portion of a sector and integrally secured thereto, said elastic tension members compensating for radial wheel expansion under temperature changes during a grinding operation.

7. A grinding wheel comprising a plurality of bonded abrasive segments arranged in spaced relation in the form of an abrasive annulus, a rotatable central support therefor which is mold ed in situ, a compressible material within the spaces between the segments which compensates for lateral expansion of the individual segments, an anchoring member embedded within each segment to secure it in position, an elongated tensioning member removably secured to each anchoring member, and means to adjustably secure each anchoring member to the support whereby each segment may be removably fastened in position under a predetermined tension and yet move radially as required by a temperature change during grinding.

8. A grinding wheel comprising a plurality of bonded abrasive segments arranged in spaced relation to each other in the form of an abrasive annulus having a cylindrical grinding face, a rotatable central support therefor which is cast in position, a compressible material located within and substantially filling the spaces between the segments and compensating for expansion of the individual segments towards each other during grinding, a plurality of anchoring members embedded within the lower portion of each segment, an elongated tensioning member removably secured to each anchoring member and slidably mounted within the central support, means engageable with the anchoring members to adjustably secure each of them to the support whereby each segment may be removably secured in position under a predetermined tension and yet be free to move radially as required by a temperature change during a grinding operation.

9. A grinding wheel comprising a plurality of separately manufactured bonded abrasive segments arranged in spaced relation in the form of a grinding annulus, a rotatable central sup port therefor which is cast in position against the bottom of the segments, a deformable material within the spaces between the segments which compensates for lateral expansion of the individual segments, anchoring members embedded within and integrally cemented to the lower portion of each segment, elongated tensioning members slidably mounted within the central support and removably secured at one end to the anchoring members, and means adjustably engageable with the other end of each tensioning member whereby each segment may be individually secured in position under a predetermined tension and compensate for radial wheel expansion during grinding.

THURE LARSSON.

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